Squaring Numbers Ending in 5

The Trick

After discussing multiplication of numbers by 11, let us discuss another math shortcut method which is very popular among kids and teenagers. This is squaring numbers ending in 5.

For kids, you can read the first portion of this post if you want to learn the trick, and read further if you want to learn the mathematics behind the trick.

Remember: it is cool if you know the trick, but it is even cooler if you know why it works. Mathematics is not just knowing the method, but also knowing the reasons.

Math Shortcut on Squaring Numbers Ending in 5 

The algorithm is squaring numbers ending in 5 is the following.

1.) Multiply the ones digits. That is 5 x 5 since they both of them in 5. Write 25 as product as shown below. The last two digits of this trick is always 25. Continue reading

The Secret of Multiplying by 11

The Math Trick: For Kids

Multiplying by 11 is probably one of the most famous mental math shortcuts.  If you have not heard of it, this math trick requires you to memorize three simple steps. To get the product of any 2-digit number multiplied by 11, for example 25 × 11, here are the steps.

Step 1: Copy the ones digit of the multiplier and make it the ones digit of the product.

In the example below, we copy 5 from 25 which is the multiplier and make it the ones digit of the product (see first figure). 

Step 2: Add the ones and tens digit of the multiplier and make it the tens digit of the product.

We add 2 and 5 and make 7 the tens digit of the product.

 

multiplying by 11

 

Step 3: Copy the tens digit and make it hundreds digit of the product.

In the example, we copy 2 from 25 and make it the hundreds digit of the product.  Continue reading